The present invention relates to antenna arrays and, more particularly, to omni-directional antenna arrays.
Radio frequency antennas are often designed as arrays to provide sufficient gain. The power feed network associated with antenna arrays, however, is often complex. The power feed network is complex because antenna pattern and gain depend on physical and network parameters. Some physical parameters include the number of elements and their spacing. Some feed network parameters include the phase and amplitude of the power signal at each of the antenna feeds as well as the impedance of the feed network delivering the power.
One omni-directional antenna array that has a relatively non-complex feed network is a co-linear coaxial antenna array. FIG. 1 shows a conventional co-linear coaxial (COCO) antenna array 100. COCO antenna 100 comprises a feed coax cable section 102, a plurality of coax cable sections 104, and a termination coax cable section 106. Connecting each section of coax 102, 104, and 106 is a wire pair 108. Wire pair 108 includes a center wire to shield wire 108a and a shield wire to center wire 108b. A power feed 110 is connected between feed coax cable section 102 and the first of the plurality of coax cable sections 104. Power feed 110 has a connection 110a to the shield of feed coax cable section 102 and a connection 110b to the shield of the first of the plurality of coax cable sections 104. Connection 110a runs to a short connection 112 internal to feed coax cable section 102, which also connects power to the center wire 114 of feed coax cable section 102. Termination coax cable section 106 similarly has a center wire 116 connected to a short 118. Other than the power feed 110 connection, feed coax cable section 102 and termination coax cable section 106 are images of each other. (Notice, determining lengths of the coaxial cable and other dimensions of the COCO antenna 100 are well known in the art and will not be explained further herein.)
The coax cable can be any conventional coax cable such as 50 ohm or 75 ohm coax cable. The coax cable can be flexible or in a semi-rigid sheath. Using 50 ohm cable, a xc2xc wave transformer may be needed in the power feed coax cable section 110. The cable sections 102, 104, and 106 are stripped and soldered to wire pairs 108 to make the connections. Moreover, the shorts 112 and 118 are located and soldered. The above example, and the description of the present invention, below, relate to conventional 50 ohm coax cable, but one of skill in the art would recognize other cable or radiating elements are possible.
The COCO antenna 100 provides an omni-directional RF antenna with a good power gain for lower frequency operation. However, the conventional COCO antenna 100, explained above, has several problems. The problems include: the construct is fragile, the electrical connections have defects, the solder placement lacks consistency, and the coax stripping is inconsistent. In general, the conventional COCO antenna 100 has a minimum error associated with its construction and handling the assembly is difficult. While these manufacturing and assembly errors can be tolerated at lower operating frequencies, at higher frequencies, such as the 5 GHz range, the errors become prohibitive. The prohibitive nature of the errors is due, in part, to the smaller lengths of coax and wires used. As the frequency increases, the wavelength, and the lengths of each section decrease. The smaller lengths of wire make the errors relatively higher, causing unacceptable degradation of the antenna pattern and gain. Also, the fragile nature of the conventional COCO antenna (coax cable sections soldered together) makes handling and assembly of the construct difficult if not prohibitive.
Thus, it would be desirous to provide a COCO antenna that had lower errors and was less fragile.
To attain the advantages of and in accordance with the purpose of the present invention, a support for an omni-directional antenna is provided. The support comprises a substrate with pre-placed transition pads and a feed pad. Coaxial cable could be soldered to the transition pads to form a co-linear coaxial antenna array.
The present invention further provides methods for designing the support including arrangement of transition pads on a substrate. A feed transition pad is also arranged on the substrate. Coaxial cable attached to the substrate at the transition pads would form a co-linear coaxial antenna array.
The foregoing and other features, utilities and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.